Micropuncture studies directed at elucidation of the physiology and pathophysiology of kidney function in several areas will be continued. Specific projects include experiments to identify and define the renal and individual nephron mechanism involved in the initial phase of hypertension when arterial blood pressure rises rapidly in 5 to 8 week old spontaneously hypertensive rats. Control studies will be done in WKY animals. Studies will continue on rats with acute renal failure following 1 hour of renal artery occlusion directed primarily at following the disturbance in excretory function in the recovery phase and determining the effects of several experimental interventions on its course. Acute unilateral denervation in volume expanded rats produces a further marked increase in urine flow from the denervated kidney which is accompanied by a decrease in salt and water excretion by the contralateral innervated kidney. Both occur without change in GFR or renal blood flow and result from reciprocal changes in the rate of tubular reabsorption. Experiments will be performed to ascertain if the increased reabsorption in the innervated kidney under this condition results from increased neural activity subsequent to denervation.